Color tunable organic electroluminescent light source

ABSTRACT

A light emitting device is provided. The light emitting device contains an array of organic light emitting diodes (OLEDs) emitting a plurality of colors, and a layer of scattering media above the light emitting surface of the OLED array. The emission color of the OLEDs may be tuned by applying different power to different sets of OLEDs. The scattering media mixes the colors from each set of OLEDs, such that the device light output has a white color having a desired color temperature.

This application claims the benefit of U.S. Provisional Application No.60/194,068, filed Mar. 31, 2000, the disclosure of which is herebyincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates generally to lighting devices and moreparticularly to an organic light emitting diode.

Organic electroluminescent devices, such as organic light emittingdiodes (OLEDs), are currently used for display applications and areplanned for use in general lighting applications. An OLED deviceincludes one or more organic light emitting layers disposed between twoelectrodes, e.g., a cathode and a light transmissive anode, formed on alight transmissive substrate. The organic light emitting layer emitslight upon application of a voltage across the anode and cathode. Uponthe application of a voltage from a voltage source, electrons aredirectly injected into the organic layer from the cathode, and holes aredirectly injected into the organic layer from the anode. The electronsand the holes travel through the organic layer until they recombine toform excited molecules or excitons. The excited molecules or excitonsemit light when they decay.

Prior art light emitting OLED display devices are currently available.One such device is described in U.S. Pat. No. 5,688,551 (the '551patent), incorporated herein by reference. An example of a prior artdisplay device 1 is illustrated in FIG. 1, which is a circuit schematicof a device similar to that described in the '551 patent. The displaydevice 1 contains an array of OLED subpixels 3. Each subpixel 3 emits aparticular color, such as red, green and blue. The device 1 contains aplurality of pixels, each of which includes a red, a green and a bluesubpixel 3. Thus, the color emitted by each pixel may be tuned byindividually controlling the power provided to each subpixel 3, and aparticular pixel may be tuned to emit white light.

The device 1 also contains a column driver circuit 5 and a row drivercircuit 7, which control the application of power to each subpixel 3. Inorder to turn on a particular subpixel 13, the column driver circuit 5must apply power to the third column in which the particular subpixel 13is located, and the row driver circuit 7 must apply power to the secondrow in which the particular subpixel 13 is located. Thus, only the onesubpixel 13 located in column three, row two emits light when power isapplied to the third column and the second row. Therefore, each subpixelin a display device receives an individual power signal and eachsubpixel in the display device is controlled separately. Furthermore,each subpixel is separately connected to a power source, since eachsubpixel has a unique row and column address.

However, the present inventor has realized that such prior art OLEDarrays, which are suitable for display devices, would suffer fromseveral disadvantages if used for general lighting applications. Theindependent subpixel control in the display device of FIG. 1 requirescomplex fabrication processes and complex driver circuits, and is thusexpensive to design and manufacture. This renders the display device ofFIG. 1 impracticably expensive for lighting applications. The presentinvention is directed to overcoming or at least reducing the problemsset forth above.

BRIEF SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, there isprovided a light emitting device, comprising an array of organic lightemitting diodes (OLEDs) emitting a plurality of colors and a layer ofscattering media above the light emitting surface of the array.

In accordance with another aspect of the present invention, there isprovided a light emitting device, comprising: (a) an array of OLEDscomprising (i) a first set of a plurality of OLEDs electricallyconnected together to the same power source such that each OLED receivesthe same power signal at the same time, the first set of OLEDs emitlight of a first color, and (ii) a second set of a plurality of-OLEDselectrically connected together to the same power source such that eachOLED receives the same power signal at the same time, the second set ofOLEDs emit light of a second color different than the first color, and(b) a power controller which provides a first amount of power to thefirst set of OLEDs and a second amount of power to the second set ofOLEDs to obtain a device light output having a desired color.

In accordance with another aspect of the present invention, there isprovided a method of generating white light, comprising providing afirst power signal having a first magnitude to a first set of pluralityof OLEDs, such that the first set of OLEDs emit light of a first color,providing a second power signal having a second magnitude to a secondset of plurality of OLEDs, such that the second set of OLEDs emit lightof a second color different than the first color, and passing the lightof the first color and the second color through a scattering medium tomix the light of the first and second colors such that the mixed lightappears white to a human observer.

In accordance with another aspect of the present invention, there isprovided a method of making a light emitting device, comprising: formingan array of OLEDs, electrically connecting a first set of OLEDs whichemit light of a first color to the same power source, electricallyconnecting a second set of OLEDs which emit light of a different secondcolor to the same power source, and forming a layer of scattering mediumover the array of OLEDs.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will be apparent from thefollowing detailed description of preferred embodiments and theaccompanying drawings, in which:

FIG. 1 is a top view of a prior art display device containing an arrayof organic light emitting diodes.

FIG. 2 is a side cross-sectional view of an array of organic lightemitting diodes containing a light scattering medium according to apreferred embodiment of the present invention.

FIGS. 3-6 are top views of arrays of organic light emitting diodesaccording to preferred embodiments of the present invention.

FIG. 7 is a side cross-sectional view of an organic light emitting diodeaccording to one preferred embodiment of the invention.

FIGS. 8-11 illustrate various examples of organic light emitting layersformed of two or more sublayers.

FIG. 12 is a side cross-sectional view of an organic light emittingdiode according to another preferred embodiment of the invention.

FIG. 13 is a bottom view of the organic light emitting diode of FIG. 12.

FIG. 14 illustrates a method of making the organic light emitting diodeof FIG. 12 according to a preferred embodiment of the present invention.

FIG. 15 illustrates a method of mounting a plurality of light emittingdevices on a mounting substrate to produce a light emitting deviceaccording to a preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present inventor has realized that, in contrast to display devices,where color mixing across different pixels and subpixels is notdesirable, color mixing in a lighting device containing an OLED array isdesirable in order to provide a smooth, uniform light for a lightingapplication. Thus, in one preferred embodiment of the present invention,a light emitting device contains a layer of scattering media above thelight emitting surface of the array. The function of this scatteringmedia is to facilitate mixing between the light emitted from theseparate OLED devices.

The present inventor has also realized that it is desirable for a lightemitting device to have a color tunable light output for generallighting applications, such as mood lighting for home or industry, orspotlights for theaters and discos. Thus, the light emitting device maybe controlled by a user or by a computer to generate a desired color ofthe light emitted by the device. In contrast to a display device, whereeach OLED is controlled independently, various sets of plurality ofOLEDs in the array are separately electrically connected so that theycan be controlled in tandem by a power controller. A desired color oflight is obtained by adjusting the power provided to the separate setsof OLEDs in the array.

I The OLED Array

A side view of a light emitting device 21 containing the OLED arrayaccording to a first preferred embodiment is illustrated in FIG. 2. Thehorizontal array contains OLED devices 23, emitting light of differentcolors, formed over a substrate 25. The term light may include UV and IRradiation in addition to visible light of different colors (i.e., ofdifferent wavelength or color temperature). In a preferred aspect of thepresent invention, the array contains OLEDs emitting red, green and bluelight (indicated by the letters R, G and B in the Figures). The lightemitting surface of the array (i.e., the top surface in FIG. 2) iscovered with a layer of scattering media 27 to promote mixing betweenthe separate colors of light emitted by the red, green and blue OLEDs.Preferably, the scattering layer 27 is placed on top of the OLEDs 23,and if desired, also in the interstitial areas between the OLEDs.

The scattering media may comprise small particles with relatively highindex of refraction that do not appreciably absorb the visible lightfrom the OLED devices. The light scattering particles may have a meanparticles size of 50 to 500 nm. Preferably, the mean particle size isbetween λ/3 and λ/2, where λ is the peak. emission wavelength of theOLEDs 23.

The preferred light scattering particles are titania, alumina, or zincoxide particles, such as the Dupont R960 TiO₂ particles coated with analumino-silicate glass having a mean particle size of 300 nanometers.However, BaTiO₃, SiO₂, CaCO₃, BaSO₄ and diamond light scatteringparticles may also be used. The scattering layer 27 may comprise a layerof packed light scattering particles or a carrier medium containing thelight scattering particles. The carrier medium may be glass or a polymermaterials, such as epoxy, silicone or urea resin. However, other carriermedium and scattering particle materials may be used, if desired.

FIG. 3 illustrates a top view of a white light emitting device 31 whichincludes the OLED 33 array tiled onto the substrate 35. The OLED devicesemit light of three different colors, such as red, green and blue, whichwhen mixed in different ratios provides different colors of white light(i.e., a white light having different color temperatures). However,other combinations of primary and/or mixed colors, such as a combinationof blue and yellow light, may be used to produce white light.

In FIG. 3, the array of OLEDs 33 is depicted as a regular array ofalternating red, green and blue OLEDs in a square pattern. However, theOLEDs may be formed in an irregular array or pattern. Furthermore, thedifferent color OLEDs may have different shapes and areas, if desired.The different OLEDs 33 can be fabricated together on the devicesubstrate 35 using patterning techniques such as shadow-masking, ink-jetprinting or screen printing. Alternatively, the different OLED 33 can befabricated separately and then physically attached onto the substrate35.

OLED devices according to the second, third and fourth preferredembodiments will now be described. The electrical connections to thevarious, OLED devices of the second through fourth preferred embodimentsare arranged such that the relative ratio of total light emitted can bevaried in order to tune the color of the emitted light. Thus, the OLEDarray of the light emitting device includes a first set of plurality ofOLEDs electrically connected together to the same power source such thateach OLED receives the same power signal at the same time. The first setof OLEDs emit light of a first color. The OLED array also includes asecond set of plurality of OLEDs electrically connected together to thesame power source such that each OLED receives the same power signal atthe same time. The second set of OLEDs emit light of a second colordifferent than the first color. The term “same power source” includes asingle power source which provides a different amount of power to thefirst and second sets of OLEDs, as well as plural power sources, each ofwhich provides the same amount of power to each OLED of one OLED set.The light emitting device also includes a power controller whichprovides a first amount of power to the first set of OLEDs and a secondamount of power to the second set of OLEDs to obtain a device lightoutput having a desired color.

FIGS. 4-6 each illustrate a top view of a light emitting deviceaccording to the second through fourth preferred embodiments,respectively, which illustrate the above concept. Preferably the devicesof the second through fourth embodiments contain the scattering media ofthe first embodiment. However, the scattering media may be omitted tosimplify device processing.

FIG. 4 illustrates a light emitting device 41 according to the secondpreferred embodiment. The device 41 includes an integrated controller42, such as a microprocessor or an ASIC chip. Alternatively, thecontroller may comprise a computer located remotely from the lightemitting device, or a wall switch or dial which is actuated by the user.

In the device 41 illustrated in FIG. 4, the first set 44 of OLEDs 43comprises a plurality of red light emitting OLEDs and the second set 45of OLEDs comprises a plurality of green light emitting OLEDs. The devicealso includes a third set 46 of a plurality of blue light emitting OLEDs43 electrically connected together to the same power source such thateach OLED receives the same power signal at the same time. In otherwords, all the OLEDs 44 which emit red light can be connected together,all the OLEDs 45 which emit green light can be connected together, andall the OLEDs 46 which emit blue light can be connected together, asillustrated in FIG. 4. In this manner, all colors from the pure red,green and blue to the various mixed whites can be obtained.

Each of the first, second and third sets of OLEDs 44, 45, 46 areconnected in parallel to their respective power source 47, 48, 49. Whilenot as preferred, the OLEDs alternatively may be connected to theirrespective power sources in series. The power sources 47, 48 and 49 maycomprise driver circuits or switches connected to an outside voltagesource, such as a power outlet or battery. Furthermore, the separatepower sources 47, 48 and 49 may alternatively comprise a single drivercircuit which is capable of simultaneously providing a different powersignal to each OLED set.

The device 41 operates as follows. The controller 42 actuates the firstpower source 47 to provide a first power signal having a first magnitudeto a first set of plurality of OLEDs 44 such that the first set of OLEDs44 emits red light of a first color. Simultaneously, the controller 42actuates the second power source 48 to provide a second power signalhaving a second magnitude to a second set of plurality of OLEDs 45, suchthat the second set of OLEDs emits green light. The controller 42 alsoactuates the third power source 49 to provide a third power signalhaving a third magnitude to a third set of plurality of OLEDs 46, suchthat the third set of OLEDs emits blue light. The tuned red, green andred light appears as white light of a desired color and colortemperature to a human observer.

FIG. 5 illustrates a light emitting device 51 according to the thirdpreferred embodiment. The OLED array in device 51 comprises a first setof OLEDs 54 which contains a plurality of red, green and blue lightemitting OLEDs 53. The array also contains a second set of OLEDs 55which contains second set of a plurality of red, green and blue lightemitting OLEDs 53. The red, green and blue light emission from the firstset of OLEDs 54 appears as a first white color light, and the red, greenand blue light emission from the second set of OLEDs 55 appears as asecond white color light different from the first white color light. Forexample, the white light emitted from the first set of OLEDs 54 has afirst color temperature, while the white light emitted from the secondset of OLEDs 54 has a different, second color temperatures. Then byseparately controlling the power from the respective power sources 57,58 to these two sets OLEDs by using the controller 52, white lighthaving any color or color temperature value between respective values ofcolor or color temperature of the white light emitted by the two sets ofOLEDs 54, 55 can be obtained.

FIG. 6 depicts a white light emitted device 61 according to the fourthpreferred embodiment of the present invention. In FIG. 6, a plurality ofOLEDs are placed in the array. The array comprises two different typesof white light emitting OLEDs. The first type of OLEDs 64 emit whitelight having a first color temperature (labeled “W1” in FIG. 6). Thesecond type of OLEDs 65 emit white light having a second colortemperature (labeled “W2” in FIG. 6) different from the firsttemperature.

Electrically, the first set of white light emitting OLEDs 64 which emitwhite light having the same first color temperature, are electricallyconnected together to the same power source 67. The second set of whitelight emitting OLEDs 65 which emit white light having the same secondcolor temperature, are electrically connected together to the same powersource 68, but separately from the first OLEDs 64. By varying the powerto the two different sets of OLEDs 64, 65, using the controller 62 allcolor temperatures between the individual OLED color temperatures can beachieved.

The white light emitting OLEDs can be made for instance using a bluelight emitting OLED device covered with a downshifting phosphor, such asthe phosphor described in U.S. application Ser. No. 60/178,451,incorporated by reference in its entirety. Preferably, the phosphorcomprises an ADE:Ce³⁺ phosphor, where A comprises at least one of Y orGd, D comprises at least one of Al, Ga or Sc and E comprises oxygen.This phosphor emits yellow light, such that the combined blue and yellowemission from the OLEDs appears as white light to a human observer. Aspecific example of such a phosphor is Y₃AI₅O₁₂:Ce³⁺ (commonly known asYAG:Ce³⁺). The preferred organic blue light emitting polymer layer in anOLED is poly(9,9-di-n-hexylfluorene-2,7-diyl). However, other phosphorsand organic light emitting materials may be suitable in theseapplications. The OLED preferably also contains a transparent ITO anodeand a LiF/Al bilayer cathode.

The different color temperatures can be obtained by using differentphosphors with the same blue OLED device. For example, by substituting Yions with Gd ions, the ADE:Ce³⁺ phosphor yellow emission shifts tolonger wavelengths. Thus, the combination of the blue OLED light and thelonger wavelength yellow light emitted by such phosphor appears as whitelight having a lower color temperature, such as a color temperature ofabout 2500K to about 5000K. In contrast, by substituting Al ions with Gaions, the ADE:Ce³⁺ phosphor yellow emission shifts to shorterwavelengths. Thus, the combination of the blue OLED light and theshorter wavelength yellow light emitted by such phosphor appears aswhite light having a higher color temperature, such as a colortemperature of about 5000K to about 8500K. Therefore, by varying thepower to OLEDs 64, 65, a device 61 white light output having a colortemperature between 2500K and 8500K can be obtained.

While the electrical contacts illustrated in FIGS. 4-6 are shown asbeing located between the individual OLEDs, the contacts may be placedin other locations. For example, the electrical contacts may be locatedon the back side of the mounting substrate, as illustrated in FIG. 15.Alternatively, the electrical contacts may be located between each OLEDand the substrate and/or over the top of each OLED. Furthermore, asillustrated in FIGS. 4-6, each OLED is connected to two row or twocolumn electrodes, to allow for common control of a plurality of OLEDs.In contrast, each subpixel 3 in FIG. 1 is connected to one row and onecolumn electrode to allow for independent subpixel control.

II. The Components of the OLED Device

The OLED described above may comprise any type of organic light emittingdiode or device. The term “light” includes visible light as well as UVand IR radiation. The device 100 according to one preferred aspect ofthe present invention is illustrated in FIG. 7. The device 100 includesan organic light emitting layer 110 disposed between two electrodes,e.g., a cathode 120 and an anode 130. The organic light emitting layer110 emits light upon application of a voltage across the anode andcathode from the voltage source “V”. The organic light emitting device100 typically includes a device substrate 125, such as glass ortransparent plastics such as PET (MYLAR®), polycarbonate, and the like,as shown in FIG. 7. The term “organic light emitting device” generallyrefers to the combination which includes the organic light emittinglayer, the cathode, and the anode, and which may also include otherelements such as the device substrate, device electrical contacts, and aphotoluminescent layer, as will be described below.

A. The Electrodes

The anode and cathode inject charge carriers, i.e., holes and electrons,into the organic light emitting layer 110 where they recombine to formexcited molecules or excitons which emit light when the molecules orexcitons decay. The color of light emitted by the molecules depends onthe energy difference between the excited state and the ground state ofthe molecules or excitons. Typically, the applied voltage is about 3-10volts but can be up to 30 volts or more, and the external quantumefficiency (photons out/electrons in) is between 0.01% and 5%, but couldbe up to 10%, 20%, 30%, or more. The organic light emitting layer 110typically has a thickness of about 50-500 nanometers, and the electrodes120, 130 each typically have a thickness of about 100-1000 nanometers.

The cathode 120 generally comprises a material having a low workfunction value such that a relatively small voltage causes emission ofelectrons from the cathode. The cathode 120 may comprise, for example,calcium or a metal such as gold, indium, manganese, tin, lead, aluminum,silver, magnesium, or a magnesium/silver alloy. Alternatively, thecathode can be made of two layers to enhance electron injection.Examples include a thin inner layer of LiF followed by a thicker outerlayer of aluminum or silver, or a thin inner layer of calcium followedby a thicker outer layer of aluminum or silver.

The anode 130 typically comprises a material having a high work functionvalue. The anode 130 is preferably transparent so that light generatedin the organic light emitting layer 110 can propagate out of the organiclight emitting device 100. The anode 130 may comprise, for example,indium tin oxide (ITO), tin oxide, nickel, or gold. The electrodes 120,130 can be formed by conventional vapor deposition techniques, such asevaporation or sputtering, for example.

B. The Organic Emitting Layer(s)

A variety of organic light emitting layers 110 can be used inconjunction with exemplary embodiments of the invention. According toone embodiment shown in FIG. 7, the organic light emitting layer 110comprises a single layer. The organic light emitting layer 110 maycomprise, for example, a conjugated polymer which is luminescent, ahole-transporting polymer doped with electron transport molecules and aluminescent material, or an inert polymer doped with hole transportingmolecules and a luminescent material. The organic light emitting layer110 may also comprise an amorphous film of luminescent small organicmolecules which can be doped with other luminescent molecules.

According to other embodiments of the invention shown in FIGS. 8-11, theorganic light emitting layer 110 comprises two or more sublayers whichcarry out the functions of hole injection, hole transport, electroninjection, electron transport, and luminescence. Only the luminescentlayer is required for a functioning device. However, the additionalsublayers generally increase the efficiency with which holes andelectrons recombine to produce light. Thus the organic light emittinglayer 110 can comprise 1-4 sublayers including, for example, a holeinjection sublayer, a hole transport sublayer, a luminescent sublayer,and an electron injection sublayer. Also, one or more sublayers maycomprise a material which achieves two or more functions such as holeinjection, hole transport, electron injection, electron transport, andluminescence.

Embodiments in which the organic light emitting layer 110 comprises asingle layer, as shown in FIG. 7, will now be described. According toone embodiment, the organic light emitting layer 110 comprises aconjugated polymer. The term conjugated polymer refers to a polymerwhich includes a delocalized π-electron system along the backbone of thepolymer. The delocalized π-electron system provides semiconductingproperties to the polymer and gives it the ability to support positiveand negative charge carriers with high mobilities along the polymerchain. The polymer film has a sufficiently low concentration ofextrinsic charge carriers that on applying an electric field between theelectrodes, charge carriers are injected into the polymer and radiationis emitted from the polymer. Conjugated polymers are discussed, forexample, in R. H. Friend, 4 Journal of Molecular Electronics 37-46(1988).

One example of a conjugated polymer which emits light upon applicationof a voltage is PPV (poly(p-phenylenevinylene)). PPV emits light in thespectral range of about 500-690 nanometers and has good resistance tothermal and stress induced cracking. A suitable PPV film typically has athickness of about 100-1000 nanometers. The PPV film can be formed byspin coating a solution of the precursor to PPV in methanol onto asubstrate and heating in a vacuum oven.

Various modifications can be made to the PPV while retaining itsluminescent properties. For example, the phenylene ring of the PPV canoptionally carry one or more substituents each independently selectedfrom alkyl, alkoxy, halogen, or nitro. Other conjugated polymers derivedfrom PPV may also be used in conjunction with exemplary embodiments ofthe invention. Examples of such derivatives of PPV include: 1) polymersderived by replacing the phenylene ring with a fused ring system, e.g.replacing the phenylene ring with an anthracene or napthalene ringsystem. These alternative ring systems may also carry one or moresubstituents of the type described above with respect to the phenylenering; 2) polymers derived by replacing the phenylene ring with aheterocyclic ring system such as a furan ring. The furan ring may carryone or more substituents of the type described above in connection withthe phenylene ring; 3) polymers derived by increasing the number ofvinylene moieties associated with each phenylene or other ring system.The above described derivatives have different energy gaps, which allowsflexibility in producing an organic light emitting layer 110 which emitsin a desired color range or ranges. Additional information onluminescent conjugated polymers is described in U.S. Pat. No. 5,247,190,which is hereby incorporated by reference.

Other examples of suitable conjugated polymers include polyfluorenessuch as 2,7-substituted-9-substituted fluorenes and 9-substitutedfluorene oligomers and polymers. Polyfluorenes generally have goodthermal and chemical stability and high solid-state fluorescence quantumyields. The fluorenes, oligomers and polymers may be substituted at the9-position with two hydrocarbyl moieties which may optionally containone or more of sulfur, nitrogen, oxygen, phosphorous or siliconheteroatoms; a C₅₋₂₀ ring structure formed with the 9-carbon on thefluorene ring or a C₄₋₂₀ ring structure formed with the 9-carboncontaining one or more heteroatoms of sulfur, nitrogen or oxygen; or ahydrocarbylidene moiety. According to one embodiment, the fluorenes aresubstituted at the 2- and 7-positions with aryl moieties which mayfurther be substituted with moieties which are capable of crosslinkingor chain extension or a trialkylsiloxy moiety. The fluorene polymers andoligomers may be substituted at the 2- and 7-positions. The monomerunits of the fluorene oligomers and polymers are bound to one another atthe 2- and 7′-positions. The 2,7′-aryl-9-substituted fluorene oligomersand polymers may be further reacted with one another to form highermolecular weight polymers by causing the optional moieties on theterminal 2,7′-aryl moieties, which are capable of crosslinking or chainextension, to undergo chain extension or crosslinking.

The above described fluorenes and fluorene oligomers or polymers arereadily soluble in common organic solvents. They are processable intothin films or coatings by conventional techniques such as spin coating,spray coating, dip coating and roller coating. Upon curing, such filmsdemonstrate resistance to common organic solvents and high heatresistance. Additional information on such polyfluorenes is described inU.S. Pat. No. 5,708,130, which is hereby incorporated by reference.

Other suitable polyfluorenes which can be used in conjunction withexemplary embodiments of the invention include poly(fluorene)copolymers, such as poly(fluorene-co-anthracene)s, which exhibit blueelectroluminescence. These copolymers include a polyfluorene subunitsuch as 2,7-dibromo-9,9-di-n-hexylfluorene (DHF) and another subunitsuch as 9,10-dibromoanthracene (ANT). High molecular weight copolymersfrom DHF and ANT can be- prepared by the nickel-mediatedcopolymerization of the corresponding aryl dibromides. The final polymermolecular weight can be controlled by adding the end capping reagent2-bromofluorene at different stages of the polymerization. Thecopolymers are thermally stable with decomposition temperatures above400° C. and are soluble in common organic solvents such astetrahydrofuran (THF), chloroform, xylene, or chlorobenzene. They emitblue light having a wavelength of about 455 nm. Additional informationon such polyfluorenes is described in Gerrit Klarner et al., “ColorfastBlue Light Emitting Random Copolymers Derived from Di-n-hexylfluoreneand Anthracene”, 10 Adv. Mater. 993-997 (1998), which is herebyincorporated by reference. Another preferred blue light emittingpolyfluorine is poly(9,9-di-n-hexylfluorine-2,7-diyl) which has a broaddouble emission peak between about 415 and 460 nm.

According to a another embodiment of a single layer device as shown inFIG. 7, the organic light emitting layer 110 comprises a molecularlydoped polymer. A molecularly doped polymer typically comprises a binarysolid solution of charge transporting molecules which are molecularlydispersed in an inert polymeric binder. The charge transportingmolecules enhance the ability of holes and electrons to travel throughthe doped polymer and recombine. The inert polymer offers manyalternatives in terms of available dopant materials and mechanicalproperties of the host polymer binder.

One example of a molecularly doped polymer comprises poly(methylmethacrylate) (PMMA) molecularly doped with the hole transportingmoleculeN,N′-diphenyl-N,N′-bis(3-methylsphenyl)-1,1′-biphenyl-4,4′-diamine (TPD)and the luminescent material tris(8-quinolinolato)-aluminum(III)- (Alq).TDP has a high hole drift mobility of 10⁻³ cm²/volt-sec, while Alq is aluminescent metal complex having electron transporting properties inaddition to its luminescent properties.

The doping concentration is typically about 50%, while the molar ratioof TDP to Alq may vary from about 0.4 to 1.0, for example. A film of thedoped PMMA can be prepared by mixing a dichloroethane solutioncontaining suitable amounts of TPD, Alq, and PMMA, and dip coating thesolution onto the desired substrate, e.g. an indium tin oxide (ITO)electrode. The thickness of the doped PMMA layer is typically about 100nanometers. When activated by application of a voltage, a green emissionis generated. Additional information on such doped polymers is describedin Junji Kido et al., “Organic Electroluminescent Devices Based onMolecularly Doped Polymers”, 61 Appl. Phys. Lett. 761-763 (1992), whichis hereby incorporated by reference.

According to another embodiment of the invention shown in FIG. 8, theorganic light emitting layer 110 comprises two sublayers. The firstsublayer 111 provides hole transport, electron transport, andluminescent properties and is positioned adjacent the cathode 120. Thesecond sublayer 112 serves as a hole injection sublayer and ispositioned adjacent the anode 130. The-first sublayer 111 comprises ahole-transporting polymer doped with electron transporting molecules anda luminescent material, e.g. a dye or polymer. The hole-transportingpolymer may comprise poly(N-vinylcarbazole) (PVK), for example. Theelectron transport molecules may comprise2-(4-biphenyl)-5-(4-tert-butylphenyl)- 1,3,4-oxadiazole (PBD), forexample. The luminescent material typically comprises small molecules orpolymers which act as emitting centers to vary the emission color. Forexample, the luminescent materials may comprise the organic dyescoumarin 460 (blue), coumarin 6 (green) or nile red. Thin films of theseblends can be formed by spin coating a chloroform solution containingdifferent amounts of PVK, electron transport molecules, and luminescentmaterials. For example, a suitable mixture comprises 100 weight percentPVK, 40 weight percent PBD, and 0.2-1.0 weight percent organic dye.

The second sublayer 112 serves as a hole injection sublayer and maycomprise poly(3,4)ethylenedibxythiophene/polystyrenesulphonate(PEDT/PSS), for example, available from Bayer Corporation, which can beapplied by conventional methods such as spin coating. Additionalinformation on holetransporting polymers doped with electrontransporting molecules and a luminescent material is described inChung-Chih Wu et al., “Efficient Organic Electroluminescent DevicesUsing Single-Layer Doped Polymer Thin Films with Bipolar CarrierTransport Abilities”, 44 IEEE Trans. on Elec. Devices 1269-1281 (1997),which is hereby incorporated by reference.

According to another embodiment of the invention shown in FIG. 9, theorganic light emitting layer 110 includes a first sublayer 113comprising a luminescent sublayer and a second sublayer 114 comprising ahole transporting sublayer. The hole transporting sublayer 114 maycomprise an aromatic amine that is readily and reversibly oxidizable,for example. One example of such a luminescent sublayer and a holetransporting sublayer is described in A. W. Grice et al, “HighBrightness and Efficiency of Blue Light-Emitting Polymer Diodes”, 73Appl. Phys. Letters 629-631 (1998), which is hereby incorporated byreference. The device described therein comprises two polymer layerssandwiched between an ITO electrode and a calcium electrode. The polymerlayer next to the ITO is a hole transport layer and comprises apolymeric triphenyldiamine derivative (poly-TPD). The blue emittingpolymer layer which is next to the calcium electrode ispoly(9,9-dioctylfluorene).

According to another embodiment of the invention shown in FIG. 10, theorganic light emitting layer 110 comprises a first sublayer 115 whichincludes luminescent and hole transport properties, and a secondsublayer 116 which includes electron injection properties. The firstsublayer 115 comprises a polysilane, and the second sublayer comprisesan oxadiazole compound. This structure produces ultraviolet (UV) light.

Polysilanes are linear silicon (Si)-backbone polymers substituted with avariety of alkyl and/or aryl side groups. In contrast to π-conjugatedpolymers, polysilanes are quasi one-dimensional materials withdelocalized σ-conjugated electrons along the polymer backbone chain. Dueto their one-dimensional direct-gap nature, polysilanes exhibit a sharpphotoluminescence with a high quantum efficiency in the ultravioletregion. Examples of suitable polysilanes include poly(di-n-butylsilane)(PDBS), poly(di-n-pentylsilane) (PDPS), poly(di-n-hexylsilane) (PDHS),poly(methyl-phenylsilane) (PMPS), and poly[-bis(p-butylphenyl)silane](PBPS). The polysilane sublayer 115 can be applied by spin coating froma toluene solution, for example. The electron injection sublayer 116 maycomprise 2,5-bis(4-biphenyl)-1,3,4-oxadiazole (BBD), for example.Additional information on UV-emitting polysilane organic light emittinglayers is described in Hiroyuki Suzuki et al, “Near-ultravioletElectroluminescence from Polysilanes”, 331 Thin Solid Films 64-70(1998), which is hereby incorporated by reference.

According to another embodiment of the invention shown in FIG. 11, theorganic light emitting layer 110 comprises a hole injecting sublayer117, a hole transporting sublayer 118, a luminescent sublayer 119, andan electron injecting sublayer 121. The hole injecting sublayer 117 andhole transporting sublayer 118 efficiently provide holes to therecombination area. The electrode injecting sublayer 121 efficientlyprovides electrons to the recombination area.

The hole injecting sublayer 117 may comprise a porphyrinic compound,such as a metal free phthalocyanine or a metal containingphthalocyanine, for example. The hole transporting sublayer 118 maycomprise a hole transporting aromatic tertiary amine, where the latteris a compound containing at least one trivalent nitrogen atom that isbonded only to carbon atoms, at least one of which is a member of anaromatic ring. The luminescent sublayer 119 may comprise, for example, amixed ligand aluminum chelate emitting in the blue wavelengths, such asbis(R-8-quinolinolato)-(phenolato)aluminum(III) chelate where R is aring substituent of the 8-quinolinolato ring nucleus chosen to block theattachment of more than two 8-quinolinolato ligands to the aluminumatom. The electron injection sublayer 121 may comprise a metal oxinoidcharge accepting compound such as a tris-chelate of aluminum. Additionalinformation on such four-layer materials and devices are described inU.S. Pat. No. 5,294,870, which is hereby incorporated by reference.

The above examples of organic light emitting layers 110 can be used todesign an organic light emitting device which emits in one or moredesired colors. For example, the organic light emitting device 100 canemit ultraviolet, blue, green, or red light.

C. The Photoluminescent Layer

As shown in FIG. 12, the organic light emitting device 200 mayoptionally include a photoluminescent layer 135. The photoluminescentlayer 135 comprises a photoluminescent material which absorbs light fromthe organic light emitting layer 110 and emits light typically having alonger wavelength. The photoluminescent material preferably comprises aninorganic phosphor, such as YAG:Ce³⁺, but may also comprise an organicphotoluminescent material such as an organic dye.

D. Sealing Member and Contacts

Referring to FIGS. 12 and 13, an organic light emitting device is shownaccording to another embodiment of the invention. The organic lightemitting device 200 comprises an organic light emitting layer 110, acathode 120, and an anode 130 which is light transmissive. The organiclight emitting device 200 also includes a device substrate 125 which islight transmissive. The elements in FIGS. 12 and 13 (e.g. the anode 130,cathode 120, light emitting layer 110) corresponding to those in FIG. 7can be formed of the same materials as described above with respect toFIG. 7. Upon application of a voltage, light (represented by arrows 101)is generated in the light emitting layer 110 and propagates through theanode 130 and the device substrate 125.

Adjacent to the cathode 120 is a sealing member 150, typicallycomprising glass, which provides a barrier to oxygen and water. Thesealing member 150, in conjunction with a sealant 152 which may compriseepoxy, a metal, or a glass frit, for example, provides a near hermeticbarrier to prevent water and oxygen penetration into the cathode 120,anode 130 and organic light emitting layer 110.

Formed adjacent to the sealing member 150 are first and second deviceelectrical contacts 162, 164, which provide electrical connections tothe anode 130 and cathode 120, respectively. As shown most clearly inFIG. 13, the first device electrical contact 162 connects electricallyto the anode 130 in a tab region 132 of the anode 130. The tab region132 is beyond the perimeter of the sealing member 150. The second deviceelectrical contact 164 connects electrically to the cathode 120 in a tabregion 124 of the cathode 120. The tab region 124 is beyond theperimeter of the sealing member 150. The organic light emitting layer110 (not shown in FIG. 13) typically occupies at least the overlapregion of the anode 130 and cathode 120 and may extend beyond theseelectrodes.

Referring again to FIG. 12, the device electrical contacts 162, 164typically have respective device contacting surfaces 163, 165 whichoccupy a common plane. These device contacting surfaces 163, 165facilitate the mounting of one or more organic light emitting devices200 onto a mounting substrate, as will be described further below inconnection with FIG. 12.

An advantageous feature of the device electrical contacts 162, 164 canbe described with reference to an imaginary surface running through thelight emitting layer 110. The imaginary surface, which is typicallyplanar, divides the organic light emitting device 200 into a first sideand a second side. The anode 130 is on the first side, and the cathode120 is on the second side. The light is emitted through the first side,and the device electrical contacts 162, 164 extend to the second side.For example, the first device electrical contact 162 extends from theanode 130 on the first side to the second side of the organic lightemitting device. The second device electrical contact 164 extends fromthe cathode 120 on the second side to another location on the secondside of the organic light emitting device. Thus, the organic lightemitting device 200 can be powered by contacting both device electricalcontacts 162, 164 on a common planar surface 163, 165 which is on anopposite side of the organic light emitting device as where the lightemission occurs. Typically the planar surface defined by surfaces 163,165 is parallel to the light emitting layer 110 and the device substrate125. This configuration allows a number of organic light emittingdevices 200 to be easily mounted adjacent to each other (“tiled”) on amounting substrate.

As shown in FIG. 13, the device substrate 125 can define the area of theorganic light emitting device 200. The first and second deviceelectrical contacts 162, 164 can occupy an area which is within the areaof the device substrate 125. Therefore, two organic light emittingdevices 200 can be placed directly adjacent to each other without anyelectrical connectors in between and with a small separation distancebetween the adjacent light emitting device substrates 125. For example,if desired, the separation distance could be less than 2 centimeters(cm), 1 cm, 0.5 cm or 0.25 cm, but is typically greater than 0.1 cm.

E. Light Scattering Layer

The organic light emitting device 200 also includes the layer of lightscattering media 145 comprising light scattering particles for effectivecolor mixing, as described above. The scattering layer 145 is preferablyformed over the top and sides of each organic light emitting device.However, if desired, the scattering layer may be formed only over thetop of each device 200, as illustrated in FIG. 12.

F. The Optional Shaped Material

In one embodiment of the present invention, an optional shapedtransparent material is formed onto the emitting surface of the deviceto improve, the device quantum efficiency. The transparent material canbe any transparent polymer or glass, for example, and can be filled withhigh index nanoparticles such that its index of refraction matches thatof the device. This reduces the Fresnel loss in the external quantumefficiency of the device. The transparent material is shaped such thatits top, light emitting, surface has dimples or corrugations whichreduce the amount of light lost through total internal reflection. Thisreduces the critical angle loss in the external quantum efficiency ofthe device.

The shaped material may be an additional layer attached to the lightemitting surface of the device substrate 125. Alternatively, the shapedmaterial may comprise the device substrate 125. The shaped transparentmaterial typically has an index of refraction which is matched to orclose to the index of refraction of the substrate or the active layer ofthe OLED device 100. The shape of the material to be attached is flat onthe side of attachment and dimpled or corrugated, for example, on theside from which light is emitted into the ambient environment. Theheight of the corrugations or dimples is typically greater than 0.1micron and typically covers the whole surface. The spacing betweendimple or corrugation peaks is typically within a factor of 10 of theirheight. The spacing does not have to conform to a regular pattern. As anexample, the shaped transparent material can be made with anythermoplastic, thermoset, or elastomer material that is transparent andcan be molded into the desired structure.

The index of refraction of the material can be adjusted to match that ofthe surface of the device 100 by the mixing of high index of refractionnanoparticles, such as TiO₂ or ZnO, into a base polymer or glassmaterial, such as epoxy. In this manner, the index of the resultingcomposite can be adjusted between the values of the pure base and thepure filler. Preferably, the size of the nanoparticles is less than 100nanometers to eliminate scattering effects and ensure transparency. Theshaped material can be attached to the light emitting surface of thedevice 100 by means of a transparent adhesive, such as an epoxy. It istypically desirable that the epoxy have close to the same index ofrefraction as that of the device 100 surface. This can be achieved byfilling the epoxy with a specific amount of nanoparticle.

In another embodiment of the present invention, the layer of scatteringmedia 145 and the index matched material comprise the same layer. Inthis embodiment, the nanoparticles having a size less than 100nanometers are mixed into the to layer of scattering media 145 to adjustthe index of refraction of the layer 145 such that it is equal to orclose to the index of refraction of the device substrate 125.Furthermore, the layer of scattering media 145 may also have a dimpledlight emitting surface in order to reduce the critical angle loss at thelight emitting surface of the layer 145.

III. Method of Making the OLED Device

FIG. 14 illustrates a method for forming the organic light emittingdevice 200 of FIGS. 12 and 13 according to an exemplary embodiment ofthe invention. As shown in FIG. 14, step 1, a glass substrate 125 issputter coated with a layer of thin indium tin oxide (ITO). The ITO isthen patterned to form the anode 130, e.g. in the pattern shown in FIG.13. In step 2, the organic light emitting layer 110 (which may includeone or more sublayers as shown in FIGS. 7-11) is deposited, for exampleby spin coating or inkjet processing. In step 3, the cathode 120 isdeposited as a reflective structure comprising a thin layer of lithiumfluoride overcoated with aluminum, for example. The cathode 120 can bedeposited through a stencil mask by evaporation, for example. Thesealing member 150, which may comprise glass, for example, is nextapplied with a sealant 152 in step 4 to form a near hermetic barrier.

In step 5, the organic light emitting layer 110 extending beyond thesealing member 150 is removed by solvent or dry etching methods. Thedevice electrical contacts 162, 164, which may comprise a metal such asaluminum or silver, are then applied to the reflective side of theorganic light emitting device 200 in step 6. The device electricalcontacts 162, 164 allow for external contact to the organic lightemitting device and additionally can provide a near hermetic seal to theanode 130, cathode 120, and light emitting layer 110. In step 7,optionally, a layer 135 of photoluminescent material, e.g. an inorganicphosphor, is applied to the device substrate 125. Optionally, a layer ofscattering particles can be applied in a subsequent step. The stepsshown in FIG. 14 are of course merely an example of a method of making alight source, and not intended to be limiting.

FIG. 15 illustrates a method of mounting one or more organic lightemitting devices onto a mounting substrate to form a light emittingdevice according to an exemplary embodiment of the invention. Step 1shows the mounting substrate 160, which may comprise a conventionalprinted circuit board such as FR4 or GETEK, or a flexible polymer filmsuch as Kapton E^(™) or Kapton H^(™) polyimide (Kapton is a trademark ofE. I. Du Pont de Nemours & Co.), Apical AV polyimide (Apical is atrademark of Kanegafugi Chemical Company), or Upilex polyimide (Upilexis a trademark of UBE Industries, Ltd) for example. In one embodiment,free-standing Kapton^(™) polyimide is mounted on a rigid frame (notshown in FIG. 15) which rigidly supports the flexible film duringprocessing and for end use if desired. An adhesive, typically comprisinga material capable of adhering at a low temperature, can be applied tothe rigid frame. Examples of suitable adhesives include materials suchas ULTEM polyetherimide (ULTEM^(™) is a trademark of General ElectricCompany) and MULTIPOSIT^(™) XP-9500 thermoset epoxy (MULTIPOSIT is atrademark of Shipley Company Inc., Marlborough, Mass.).

In step 2, according to one embodiment, another adhesive 161, which istypically organic, such as ULTEM^(TM), SPIE (siloxane polyimide epoxy)or other polyimide and epoxy blends, or cyanoacrylate is applied to themounting substrate. 160, as shown in FIG. 15. In step 3, one or moreorganic light emitting devices 200 are placed on the adhesive 161, andthe adhesive is cured to bond the organic. light emitting devices 200 tothe mounting substrate 160.

In step 4, vias 169 are formed using laser ablation or reactive ionetching, for example, through the mounting substrate 160 and theadhesive 161 to the device contacting surfaces 163, 165 of the deviceelectrical contacts 162, 164, respectively. In step 5, first and secondmounting electrical contacts 172, 174 are formed or inserted into thevia holes 169 to make contact with the device electrical contacts 162,164, respectively. The mounting electrical contacts 172, 174 can beformed as a patterned metal layer using sputter or electroless platingtechniques, in combination with electroplating if desired, and patternedwith a standard photoresist and etch process. The interconnectmetallization in one embodiment comprises a thin adhesion layer of 1000angstroms (Å) sputtered titanium, coated by a thin layer of 3000 Åsputtered copper, coated by a layer of electroplated copper to athickness of 4 microns, for example. An optional buffer layer of 1000 Åof titanium can be applied over the electroplated copper. The mountingelectrical contacts 172, 174 can also be applied by the conventionalmethods of evaporation with a shadow mask or screen printing.

In step 6, the scattering layer 145 can be applied to organic lightemitting devices 200 individually, or more typically can be appliedacross a number of organic light emitting devices 200, as shown in FIG.15. Although not shown in step 6, a nonconductive material such as SPIE(siloxane polyimide epoxy) can be inserted into the gaps 175 betweenadjacent organic light emitting devices 200.

Although only two OLEDs 200 are shown in FIG. 15 for ease ofillustration, this method is preferably used to make large area lightemitting devices comprising many individual OLEDs 200. For example, alarge area light emitting device, such as a 2 ft. by 2 ft. device, maybe formed by attaching a plurality of individual OLEDs 200 to a mountingsubstrate 160 using the method described above or other mountingmethods. This is advantageous in forming a large area light emittingdevice because the device is not limited by the size of the substrateused to make each OLED, in contrast to the display device of the '551patent in which all the OLEDs are fabricated on the same glasssubstrate. Thus, the size of the display device of the '551 patent islimited by the size of the glass substrate. While mounting ofprefabricated OLEDs to the mounting substrate, as illustrated in FIG. 15is preferred, in an alternative aspect of the present invention, allOLEDs of the light emitting device may be directly fabricated on thesame substrate.

Although embodiments of the present invention allow the organic lightemitting devices 200 to be placed very close to each other on themounting substrate 160, it may be desirable in some applications to havea larger spacing between individual organic light emitting devices 200.In such cases, it is desirable to also place the scattering layerbetween organic light emitting devices 200.

Spacing between organic light emitting devices 200 may also occur in thecase where the mounting substrate 160 is designed to be flexible,curved, or non-planar. The mounting substrate 160 may be formed in anydesired shape, e.g. to conform to an existing building structure. Afterthe mounting electrical contacts have been installed, they can beconnected to a suitable power supply, as illustrated in FIGS. 3-5, forexample.

Other embodiments of the invention will be apparent to those skilled inthe art from a consideration of the embodiments disclosed herein. It isintended that the specification and examples be considered as exemplaryonly, with the scope and spirit of the invention being defined by thefollowing claims.

What is claimed is:
 1. A light emitting device, comprising: an array oforganic light emitting diodes (OLEDs) emitting a plurality of colors,said array comprising a plurality of groups of OLEDs, each of said groupbeing capable of being controlled to emit at least one of said colors;and a scattering medium disposed adjacent to a light-emitting surface ofthe array.
 2. The device of claim 1, wherein an emission from the deviceappears as white light to a human observer.
 3. The device of claim 2,wherein: each OLED emits light of a first color; and further comprisinga luminescent material over each OLED, said luminescent materialemitting light of a second color.
 4. The device of claim 3, wherein theOLEDs emits blue light and the luminescent material comprises a phosphorwhich emits yellow light, such that the OLED appears to emit white lightto a human observer.
 5. The device of claim 4, wherein the OLED arraycomprises: a first set of OLEDs comprising a plurality of OLEDs coveredwith a first phosphor which emit white light having a first colortemperature; and a second set of OLEDs comprising a plurality of OLEDscovered with a second phosphor which emit white light having a secondcolor temperature different from the first color temperature.
 6. Thedevice of claim 5, wherein: the first set of OLEDs are electricallyconnected together to a power source such that each OLED receives thesame power signal at the same time; and the second set of OLEDs areelectrically connected together to a power source such that each OLEDreceives the same power signal at the same time.
 7. The device of claim6, further comprising a power controller which provides a first amountof power to the first set of OLEDs and a second amount of power to thesecond set of OLEDs to obtain a device white light output having adesired color temperature.
 8. The device of claim 1, wherein the OLEDarray comprises: a first set of a plurality of OLEDs emitting aplurality of different colors, electrically connected together to thesame power source such that each OLED receives the same power signal atthe same time; and a second set of a plurality of OLEDs emitting aplurality of different colors, electrically connected together to thesame power source such that each OLED receives the same power signal atthe same time.
 9. The device of claim 8, wherein: the plurality ofcolors comprises red, green and blue colors; and the red, green and bluelight emission from the first set of OLEDs appears as a first whitecolor light, and the red, green and blue light emission from the secondset of OLEDs appears as a second white color light different from thefirst white color light.
 10. The device of claim 9, further comprising apower controller which provides a first amount of power to the first setof OLEDs and a second amount of power to the second set of OLEDs toobtain a device light output having a desired white color.
 11. A lightemitting device comprising: an array of organic light emitting diodes(OLEDs) emitting a plurality of colors, said array comprising aplurality of groups of OLEDs, each of said group being capable of beingcontrolled to emit at least one of said colors, wherein the arraycomprises: a first set of a plurality of a first color light emittingOLEDs electrically connected together to a first power source such thateach OLED of said first set receives the same power signal at the sametime; and a second set of a plurality of a second color light emittingOLEDs electrically connected together to a second power source such thateach OLED of said second set receives the same power signal at the sametime.
 12. The device of claim 11, further comprising: a third set of aplurality of a third color light emitting OLEDs electrically connectedtogether to a third power source such that each OLED of said third setreceives the same power signal at the same time; and wherein the firstcolor comprises red, the second color comprises green and the thirdcolor comprises blue.
 13. The device of claim 12, further comprising apower controller which provides a first amount of power to the first setof OLEDs, a second amount of power to the second set of OLEDs and athird amount of power to the third set of OLEDs to obtain a combineddevice light output having a desired color.
 14. A light emitting devicecomprising: an array of organic light emitting diodes (OLEDs) emitting aplurality of colors, said array comprising a plurality of groups ofOLEDs, each of said group being capable of being controlled to emit atleast one of said colors, wherein said light emitting device furthercomprises a layer of scattering medium that comprises particles thatscatter in a substantially unattenuated manner visible light emitted bythe OLEDs.
 15. The device of claim 14, wherein the scattering particlescomprise a material selected from the group consisting of titania,alumina, and zinc oxide; said scattering particles being located aboveand between the OLEDs.
 16. The device of claim 15, wherein thescattering particles comprise titania particles coated with analumino-silicate glass having a mean particle size of about 300 nm. 17.A light emitting device, comprising: (a) an array of OLEDs comprising:(i) a first set of a plurality of OLEDs electrically connected togetherto the same power source such that each OLED receives the same powersignal at the same time, the first set of OLEDs emit light of a firstcolor; and (ii) a second set of a plurality of OLEDs electricallyconnected together to the same power source such that each OLED receivesthe same power signal at the same time, the second set of OLEDs emitlight of a second color different than the first color; and (b) a powercontroller which provides a first amount of power to the first set ofOLEDs and a second amount of power to the second set of OLEDs to obtaina device light output having a desired color.
 18. The device of claim17, wherein the controller provides power to each set of OLEDs to obtaina device light output having a desired white color.
 19. The device ofclaim 18, wherein: the first set of OLEDs comprises a plurality of redlight emitting OLEDs; the second set of OLEDs comprises a plurality ofgreen light emitting OLEDs; and further comprising a third set of aplurality of blue light emitting OLEDs electrically connected togetherto the same power source such that each OLED receives the same powersignal at the same time.
 20. The device of claim 18, wherein: the firstset of OLEDs comprises a plurality of red, green and blue light emittingOLEDs; the second set of OLEDs comprises a second set of a plurality ofred, green and blue light emitting OLEDs; and the red, green and bluelight emission from the first set of OLEDs appears as a first whitecolor light, and the red, green and blue light emission from the secondset of OLEDs appears as a second white color light different from thefirst white color light.
 21. The device of claim 18, wherein the OLEDscomprise blue light emitting OLEDs covered with a ADE:Ce³⁺ phosphor,where A comprises at least one element selected from the groupconsisting of Y and Gd, D comprises at least one element selected fromthe group consisting of Al, Ga, and Sc and E comprises oxygen, and whichemits yellow light, such that the OLEDs appear to emit white light to ahuman observer.
 22. The device of claim 21, wherein: the first set ofOLEDs contains the ADE:Ce³⁺ phosphor having a first composition, thefirst set of OLEDs emitting white light having a first colortemperature; a second set of OLEDs contains the ADE:Ce³⁺ phosphor havinga second composition, the second set of OLEDs emitting white lighthaving a second color temperature different from the first colortemperature; and the desired light output having a desired white colorcomprises a light output having a desired color temperature.
 23. Thedevice of claim 17, further comprising: (c) a layer of scattering mediaabove a light emitting surface of the OLED array.
 24. The device ofclaim 23, wherein the layer of scattering media comprises particleswhich scatter but do not appreciably absorb visible light emitted by theOLEDs.
 25. The device of claim 24, wherein the scattering particlescomprise titania, alumina or zinc oxide particles located above andbetween the OLEDs.
 26. The device of claim 24, wherein the plurality ofseparate OLEDs is attached to a common mounting substrate.
 27. Thedevice of claim 26, wherein each OLED comprises: a transparent substratebelow the layer of scattering media; a transparent electrode below thetransparent substrate; an organic polymer or molecular light emittinglayer below the transparent electrode; a metal electrode below the lightemitting layer; a sealing member below the metal electrode; metal devicecontacts contacting the transparent and metal electrodes, havingportions located below the sealing member; and further comprising: anadhesive layer on the mounting substrate supporting the array of OLEDS,such that the metal device contacts of each OLED are mounted over theadhesive layer; and electrical contacts contacting the metal devicecontacts through the mounting substrate.
 28. The device of claim 27,further comprising a shaped material, which comprises the transparentsubstrate or a transparent material attached to the transparentsubstrate, and which contains: (i) nanoparticles having a size of lessthan 100 nm which adjust an index of refraction of the output couplersuch that it is equal or close to the index refraction of the organiclight emitting diode; and (ii) a dimpled light emitting surface.
 29. Amethod of generating white light, comprising: providing a first powersignal having a first magnitude to a first set of plurality of OLEDs,such that the first set of OLEDs emit light of a first color; providinga second power signal having a second magnitude to a second set ofplurality of OLEDs, such that the second set of OLEDs emit light of asecond color different than the first color; and passing the light ofthe first color and the second color through a scattering medium to mixthe light of the first and second colors such that the mixed lightappears white to a human observer.
 30. The method of claim 29, whereinthe steps of providing the first and second power signals comprisesproviding a first amount of power to the first set of OLEDs and a secondamount of power to the second set of OLEDs to obtain a device lightoutput having a desired color temperature.
 31. The method of claim 30,further comprising controlling the amount of power provided to the firstand second sets of OLEDs to generate white light having the desiredcolor temperature.
 32. The method of claim 29, wherein: the step ofemitting the first color light comprises emitting red light; the step ofemitting the second color light comprises emitting green light; andfurther comprising emitting blue light from a third set of OLEDs andpassing the blue light through the scattering medium to mix the red,green and blue light, such that the mixed light appears white to a humanobserver.
 33. The method of claim 29, wherein: the step of emitting thefirst color light comprises emitting white light having a first colortemperature; the step of emitting the second color light comprisesemitting white light having a second color temperature; and the mixedlight comprises white light having a color temperature value between thefirst and second color temperature values.